The invention relates to processes and apparatus for surrounding foam mold patterns with sand.
Various methods are known for surrounding a foam mold pattern in a mold flask with sand. Such methods include (a) depositing sand relatively uniformly across the mold flask, such as through a screen, (b) inserting tubes into the corners of the mold flask and releasing sand through the tubes into the mold flask, (c) inserting the foam pattern into a mold flask of fluidized sand, and (d) manually filling the mold flask.
Manually filling the mold flask is undesirable for obvious reasons. Inserting the foam pattern into fluidized sand often causes distortion of the foam pattern due to insertion forces and the large amount of sand settling that takes place when the fluidizing is discontinued. This method also requires expensive equipment for fluidizing sand. The other two methods are generally acceptable, except that they present problems when the foam mold pattern is thin walled and has an inner cavity. In such a case, when the tube method is used, the mold flask fills with sand outside the foam pattern before the inner cavity fills with sand. Therefore, before the inner cavity fills with sand, a pressure gradient forms across the wall of the foam pattern. The result is a large exterior force on the foam pattern, which might distort or crush the pattern.
When the screen or even distribution method is used, the mold flask outside of the foam pattern and the inner cavity fill at the same time. However, if the walls of the foam pattern around the inner cavity are not substantially vertical so that the inner cavity of the foam pattern fills more slowly or more quickly than the mold flask outside the foam pattern, such as in the case of a hollow cone, a pressure gradient will still form across the wall of the foam pattern.
Attention is directed to the following U.S. patents: Wuelfing U.S. Pat. No. 523,392, issued July 24, 1894; Small U.S. Pat. No. 1,433,663, issued Oct. 31, 1922; Rosenthal U.S. Pat. No. 2,283,093, issued May 12, 1942; and Warner U.S. Pat. No. 3,967,662, issued July 6, 1976.